US3440194A - Wax composition containing ethylene vinyl acetate or ethylene ethyl acrylate and a graft copolymer of ethylene with maleic acid - Google Patents

Description

United States Patent 3,440,194 WAX COMPOSITION CONTAINING ETHYLENE VINYL ACETATE OR ETHYLENE ETHYL AC- RYLATE AND A GRAFI COPOLYMER OF ETHYLENE WITH MALEIC ACID Frank J. Taranto, Flushing, and Herman F. Weindel, Uniondale, N.Y., assignors to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Oct. 20, 1964, Ser. No. 405,260 Int. Cl. C08f 29/50, 45/52 US. Cl. 260-285 14 Claims ABSTRACT OF THE DISCLOSURE Coating compositions are provided comprising petroleum wax, an interpolymer selected from the group consisting of interpolymers of ethylene and vinyl acetate and interpolymers of ethylene and ethyl acrylate, and graft copolymers of polyethylene and a dicarboxylic acid or anhyride thereof.

This invention has to do with waxand polymer-containing compositions for coating paper, cardboard, cartons and the like. More specifically, the invention is particularly directed to such compositions of exceptional heat seal strength characteristics.

Packaging of foodstuffs in recent years has given rise to a need for new containers adapted to meet a specific standard or adaptable for use under a diversity of severe conditions. Thus, paperboard cartons used for packaging of bacon and like products should be capable of being heat sealed and should have significant heat seal strength. That is, plies of paperboard suitably coated are held together under light pressure, as about A to 3 pounds per square inch, and are heated to about ZOO-425 F. to seal the plies one to another. As contemplated herein, significant heat seal characteristics denote a seal strength value of at least about 75 grams per inch obtained when two 25 pound glassine (a thin, dense translucent paper) strips, previously coated and heat sealed to one another at a temperature from about 200 F. to about 250 F. by a heat sealer, are delaminated on an Instron tester at 70 F. and at a rate of 5 inches per minute. A suitable heat sealer is Model 12 AS, Sentinel Laboratory Heat Sealer, made by Packaging Industries.

Some wax-polymer coating compositions known to date have significant heat seal characteristics in addition to such other desired characteristics as: toughness, scuff resistance and initial gloss. Yet, such compositions fail to meet one or more other requirements. By Way of illustration, blends of wax and homopolymers of ethylene, propylene, isobutylene and isoprene exhibit toughness, scuff resistance and intitial gloss; the same blends fail to have significant heat seal strength. In contrast, blends of wax and copolymers of ethylene and vinyl acetate or ethyl acrylate have significant heat seal strength; but such blends suffer from poor gloss retention, excessive softness and poor slip characteristics. Gloss retention is evidenced by the extent of material exuding from a coated carton after storage at 105 F. for at least one week.

It is an object of this invention, therefore, to provide modified wax coating compositions having significant heat seal characteristics, as defined above. Still another object is to provide such coating compositions which are hard, compatible, retain gloss, and have good slip characteristics. Additional objects will be apparent from the following description.

Accordingly, the compositions of this invention which meet the foregoing objects, comprise:

Petroleum wax An interpolymer containing from about 77 to about 85 3,440,194 Patented Apr. 22, 1969 percent by weight of ethylene and from about 23 to about 15 percent by weight of vinyl acetate, or an interpolymer containing from about 70 to about percent by weight of ethylene and from about 30 to about 20 percent by weight of ethyl acrylate, and

A graft copolymer comprising a dicarboxylic-acid-rnodified polyethylene,

proportions of the named components being so balanced as to have a seal strength when applied to glassine of at least about 75 grams per inch. Outstanding compositions are provided by balancing proportions in keeping with the following tabulation:

Component: Percent," weight Petroleum wax 47.5-82.5 Copolymer 10-40 Graft copolymer 5-15 It is desirable to incorporate a minor amount, from about 10 to about 500 parts per million, of a petroleumwax-soluable, phenolic antioxidant in the compositions to provide protection against oxidation. Particularly suitable is 2,6-di-tertiarybutyl-p-cresol, marketed as Tenox BHT by Eastman Chemical. Another suitable antioxidant comprises a mixture of 2-tertiarybutyl-4-hydroxyanisole and 3-tertiarybuyl-4-hydroxyanisole, similarly marketed as Tenox BHA.

Petroleum waxes contemplated herein include paraffin Waxes, microcrystalline waxes and intermediate waxes. Particularly preferred, however, are blends of parafiin and microcrystalline waxes.

Paraffin waxes used herein have a melting point from about F. to about 160 F. Preferred, however, are those having a melting point above about F., particularly for gloss stability purposes.

The microcrystalline wax, or mixtures of two or more of such waxes, are obtained from heavy distillate oils or residual lubricating oils by well-known precipitation procedures. The waxes are obtained from solvent solution by cooling the solution to a temperature range of about 4060 F., the Wax product melting at about 170 F. Conventional microcrystalline wax can be considered to be comprised of two components. A ceresin Wax component is composed predominantly of normal and slightly branched parafiins, and has a melting point of the order of ISO-200 F. The lower melting point plastic component, melting points being in the range of 150-180 F., is composed of highly branched and cyclic hydrocarbons. When one microcrystalline wax is present in the compositions of this invention, it is preferred that it have a melting point of the order of -170 F. and that it be a laminating grade. In general, then, laminating grades (ISO- F., melting point) are preferred; however, coating grades of microcrystalline wax can be used.

With regard to the interpolymer or mixture of interpolymers, a critical feature obtains in the content of unsaturated ester. As indicated, the interpolymer is formed of ethylene and vinyl acetate or ethyl acrylate. When vinyl acetate is present in the interpolymer or mixture of interpolymers, the monomer concentration thereof should not exceed 23 percent, by weight, the balance comprising ethylene. The monomer concentration of vinyl acetate, then, is from about 15 to 23 percent by weight. Thus, an individual vinyl acetate/ethylene interpolymer having a vinyl acetate concentration of 17-19 percent by weight can be used. So also can a mixture of this particular interpolymer and a related interpolymer in which the vinyl acetate is about 28 percent by weight, so long as the average vinyl acetate content is not in excess of 23 percent by weight.

Particularly preferred ethylene/vinyl acetate copolymers for the compositions of this invention are: one having an ethylene/vinyl acetate comonomer ratio of 3 4 about 81-83/ 19-17 and a melt index of about 125-175, terial is a polyethylene modified with a minor amount such as Elvax 420; and another having substantially the of maleic acid, as marketed by Eastman Chemical as same comonomer ratio and a melt index of about 2.5-3.5, Epolene C-16. The latter has the following properties: such as Elvax 460. Another such copolymer is DQD 6225 which has an ethylene/vinyl acetate comonomer ratio of l Welght, number average, PP 7,000 about 82/18 and a melt index of about 145. When mix- 5 Viscosity, Brookfield, cps. 149 C 12,500 tures are used such that a copolymer of vinyl acetate Tensile Strength, psi 800 content in excess of 23 percent is included, suitable ones Ring & ball Softenlng P011111 (ASTM are Elvax 220 and Elvax 250. Elvax 220 has a melt index C- 106 of 125-175 and Elvax 250 a corresponding index of Penetration hardness, tenths of 12-18; each has an ethylene/vinyl acetate cornonomer 2 C-) ratio of 7173/2927. Similarly, DQD 3269 can be used in such mixtures; this has an ethylene/vinyl acetate co- The graft copolymers can be formed by methods monomer ratio f about 72/28 and a melt index of known in the art, such as those shown in the text Block 23 The Elvax copolymers are made by L du Pom de and Graft Copolymers, of Burlant and Hoffman; Rein- Nemours and the DQD copolymers are marketed by hold? 1960- Union Carbide Still other adjuvants can be included in the new com- As indicated, interpolyiners of ethylene and ethyl acry- POSIUOPS to lmpart P P P Wlthout late are also contemplated herein. These are characterized detractmg 9 the Propertles achleved f the by an ethylene/ethyl acrylate comonomer ratio of about Ponents reqmred namelyt Petroleum Wax, mterpolyr'ner 0 30 to about 80/20 Typical of such copolymers and graft copolymer. These include: polyethylene, polyiso- Dow Chemical products EA 2018 and EA 3018, the butylene, butyl rubber, slip agents such as 9-octadecenformer having a comonomer ratio of 80/20 and the latter amlde and reslnous such as Polyterpenes and a ratio of 70/30, with each having a melt index of 18; Pantaerythntol esters of and Union Carbide products DPDB 6169 and DQDA In Table I below, compositions of this invention and 2100 Natural, the former having a eomonomer ratio of related compositions are shown in order to illustrate the 82/18 and a melt index of 6 and the latter being a purified unusual and critical nature of the new compositions. Seal form of the former. Particularly preferred is EA 3018. strimgth on glassme was dFFermmed by technlque f A third component f the new compositions is a graft scribed above. Glossstability was determined by noting copolymer comprising a dicerboxylic acid modified poly the extent of material exuding to the coatmgsurface ethylene. The dicarboxylic acid modifier is unsaturated, frofn f f Coated Wlth a composltlon after havlng i being typified by maleic acid and fumaric acid. Preferably, malntalned an n f0r 7 days at 105 F. Compatibility the acid is maleic acid. The modifier represents a minor was determlned y allowlng the blends to Stand With ut amount of the graft copolymer. It is to be understood, agitation in an Oven at 300 F. for the time intervals however, that the acid or anhydride thereof can be used indicated. to form the modified polyethylene. An outstanding rna- The results are shown in Table I following.

TABLE I Run 1 2 6 7 8 9 11 12 13 Composition:

Parafiin Wax, 150 F., M.I 55 Microcrystalliiie Wax.. 10 10.. Copolymer 1 B Copolymer 2 e Copolymer 3 a copolymer 4 a 1 Graft Copolymer 1 Polyethylene b Oxidized Polyethylene c Copolymer 5 Copolymei' 0 Compatability at 300 1 2% days Clear Clear Clear Clear Clear... Clear Slight liaze. 4% days.

.do "do..." do ..d0 do. do do do.... Do. Gloss Stab'lity Excellent Excellent" Poor (mas- Exeellent Excellent" Excellent Excellent" Excellent Satisfactory.

sive exu- (latiori). Seal Strength 011 Glassine,

gmJin 124 101 9 40 8 71 17 44 172.

Composition:

Paraifin Wax, F., M.P. 55 55 55 55 55 55 55 55. Microcrystallirie Wax 10 10.

Copolyi'ner 1 a 1 Copolynier 2 Gopolymer 3 Copolymer 4 I1 Graft Copolymer 1 Polyethylene b Oxidized Polyethylene Copolymer 5 a Copolym Compatability at 300 F.:

2% days Segaretes into Olear Hazy Clear Clear Clear Clear Clear.

p iases.

4% days do do do .do do d0 "do D0.

Gloss Stability Poor (massive Excellent.-- Satisfactory-.. Poor (massive Excellerit Exeellent.. Excellent Excellent.

exudation) exudation) Seal Strength on Glassirie,

gin/in 108 64 137 203 80 8.

= Copolymer lzElvax 420; Copolymei- 2:Elvax 460; 00- b Epolene N-10. molecular weight 1,500 (number average).

polymer 3:1Glvax 220; Copolyniei- 4:Elvax 260; Copolyiner AC G29; oxidized polyethylene,

5 13A 2018; copolymer G EA 3018; Graft Copolynier lzEpoleiie C-IG.

Results given in Table I reveal that the compositions of Run Nos. 1 and 2, typical of the new compositions, have unusually high seal strength values, 124 and 101, respectively. By way of comparison, Run No. 6 indicates that the omission of a graft copolymer and a corresponding increase in copolymer (or interpolymer) content results in almost a complete loss in seal strength and loss in gloss. Run No. 7 indicates that omission of the copolymer and a corresponding increase in a graft copolymer concentration results in a substantial loss in seal strength. Thus, a comparison of Run Nos. 1, 6 and 7 would indicate that the seal strength value expected by modification of the compositions of Run Nos. 6 and 7 would be of the order of 50; unexpectedly, it is 124. Moreover, the composition of Run No. 1 is marked by good compatibility and excellent gloss stability.

Run No. 8 shows that replacement of the graft copolymer with a like amount of polyethylene, results in almost complete loss in seal strength.

Run No. 9 reveals that substitution of an oxidized polyethylene for a like amount of graft copolymer causes a material loss in seal strength. However, a distinct deficiency of the composition of Run No. 9 is its undesirable odor, imparted by the oxidized polyethylene. This makes the composition unsuitable for use as a coating for a food package.

Run No. 11 shows that omission of a copolymer from the composition of Run No. l and replacement with a like amount of the oxidized polyethylene, results in almost complete loss of seal strength.

Run No. 12 can be compared with Run No. 1, since polyethylene is used in place of the copolymer. Here again, seal strength is unsatisfactory.

Run No. 13 shows another composition of the invention, the composition being marked by an excellent seal strength value of 172.

Run No. 14 is compared with Run No. 1, since the copolymer used has a vinyl acetate content of 28 percent by weight. While a significant heat seal value is obtained, gloss stability is poor as evidenced by massive exudation, and the composition is marked by incompatibility.

Run No. 15 shows that reversing of the concentrations of copolymer and graft copolymer, thereby providing an excess of the latter, produces a seal strength only half as great as in Run No. 1.

Run No. 16 illustrates the use of a mixture of copolymers, one having a vinyl acetate content of about 17-19 percent and the other of about 28 percent, and the mixture having an average of 23 percent. Excellent seal strength is realized.

Run No. 18 illustrates that a composition containing a copolymer of 28 percent vinyl acetate, and in which a graft copolymer is not present, has a most satisfactory seal strength value. However, massive exudation evidences unsatisfactory gloss retention.

Run Nos. 20, 21 and 22 illustrate other compositions contemplated herein. The copolymers used comprise ethyl acrylate and ethylene. Comparison of Run Nos. 21 and 22 shows that reversal of the copolymer and graft copolymer concentrations causes a decrease in seal strength, yet both values are satisfactory.

Run No. 23 illustrates that a composition containing a large concentration of ethyl acrylate copolymer and no graft copolymer has substantially no seal strength.

The coating compositions of this invention are particularly useful in folding carton applications, especially for packaging of butter, oleomargarine, ice cream, frozen foods, bacon and related meat products. They are also useful for coating of paper, film, foil and other substrates. Other uses include curtain coating and lamination of a variety of materials.

This invention has been described with reference to preferred compositions and components therefor. However, it is to be understood that departure from the preferred embodiments can be made within the scope of the specification and claims.

We claim:

1. A coating composition comprising in approximate percent by weight:

Petroleum wax having a melting point from about F. to about 160 F An interpolymer selected from the group consisting of an interpolymer containing from about 77 to about 85 percent by weight of ethylene and from about 23 to about 15 percent by weight of vinyl acetate, and an interpolymer containing from about 70 to about 80 percent by weight of ethylene and from about 30 to about 20 percent by weight of ethyl acrylate A graft copolymer comprising Polyethylene modified with a minor amount of maleic acid proportions of the named components being so balanced that the composition has a seal strength when applied 'to glassine of at least about 75 grams per inch.

2. A composition as defined by claim 1 wherein the petroleum wax is a parafiin wax having a melting point above about F.

3. A composition as defined by claim 1 wherein the petroleum wax is a parafiin wax having a melting point of about F.

4. A composition as defined by claim 1 wherein the petroleum wax comprises a mixture of a parafiin wax having a melting point above about 135 F. and a laminating-grade microcrystalline wax having a melting point from about 150 F. to about 170 F.

5. A composition as defined by claim 4 wherein the microcrystalline wax has a melting point of about F.

6. A composition as defined by claim 1 wherein the interpolymer has a comonomer ratio, weight percent, ethylene/vinyl acetate of about 82/18, and a melt index of 125-175.

7. A composition as defined by claim 1 containing a mixture of interpolymers of ethylene and vinyl acetate, the vinyl acetate monomer content, weight percent, of the mixture being at least about 15 and up to about 23.

8. A composition as defined by claim 1 wherein the interpolymer has a comonomer ratio, weight percent, ethylene/ethyl acrylate of about 70/30 and a melt'index of about 18.

9. A composition as defined by claim 1 wherein the graft copolymer comprises polyethylene modified with about 0.7 percent, by weight of maleic acid.

10. A composition as defined by claim 1 wherein the graft copolymer has a molecular weight of about 7000.

11. A coating composition comprising in approximate percent by weight:

12. A coating composition comprising in approximate percent by weight:

Paraffin wax, M.P., 150 F. Microcrystalline wax, M.P., 165-170 F. An interpolymer as defined in claim 1 and having a comonomer ratio, weight percent, ethylene/ethyl acrylate of about 70/ 30 and a melt index of about 18 25 A graft copolymer as defined in claim 1 10 7 8 13. A coating composition comprising in approximate 3,025,167 3/1962 Butler 26028.5 percent by weight: 3,146,214 8/ 1964 Jakaitis et al. 260-28.5 o 3 201 498 8/1965 Brunson et al 260897 Paraffin wax, M.P., 150 F. 55 Microcrystalline wax, M.P., 165-170 F 10 3,355,405 11/1967 Tyran 260'-28-5 A graft copolymer as defined in claim 1 10 5 FQREIGN PATENTS A mixture of about equal percentages of an interpolymer having a comonomer ratio, weight percent, 643,353 2/ 1964 Belglllmethylene/vinyl acetate of about 82/18 and a melt OTHER REFERENCES index of about 125-175, and of an interpolymer having a comonomer ratio, weight percent, ethyl- 10 Epolene C-16 Technical Data Publication TDS No. ene/ vinyl acetate of about 72/28 and a melt index F-128, 6 pages (1963) Eastman Chemical Products, Inc. of about 125-175 25 Eastman Technical Data Epolene C-16 as a Petroleum 14. A coating composition as defined by claim 1 con- Wax Modlfier TDS F429 February 1964 5 taining from about 10 to about 500 parts per million of a petroleum-wax-soluble, phenolic antioxidant. 15 MORRIS LIEBMANPfimary Examine"- References Cited H. S. KAPLAN, Assistant Examiner.

UNITED STATES PATENTS US. Cl. X.R.

2,766,214 10/1956 Erchak 26028.5 20 260897 2,877,196 3/1959 Reding 260-285